1. Field of the Invention
The present invention relates to a suspension system for anchoring wheels used for steering to a frame of a vehicle.
2. Description of Related Art
Hereinafter, a fore-to-aft direction of the vehicle is referred to as a longitudinal direction, and a side-to-side direction of the vehicle is referred to as a transverse direction. Also, a location near a centerline of the vehicle is referred to as an inside location, and a location distant from a centerline of the vehicle is referred to as an outside location.
A double pivot type suspension system for a vehicle is known. For example, Japanese Utility Model Laid-Open publication No. 64-26507 shows such a type of suspension system. This type of suspension system comprises a steering knuckle for supporting a wheel, and an upper arm and a lower arm respectively connecting an upper portion and a lower portion of the steering knuckle to a frame of a vehicle. At least one of the arms comprises two link members, each of which is pivotally connected to the frame at one respective end thereof, and to the steering knuckle at an opposite respective end thereof.
In this type of suspension system, a kingpin axis, which is an axis around which a wheel used for steering is turned, extends through a cross point between the axes of the two link members. The kingpin axis moves in response to movement of the cross point in a horizontal plane during steering of the vehicle.
When the vehicle is turned, a wheel which is located radially inwardly in relation to a turning circle must be turned more sharply than a wheel which is located radially outwardly in relation to the turning circle. This principle is known as the ACKERMAN PRINCIPLE. The ACKERMAN PRINCIPLE has previously been achieved by differentiating a transverse inclination in a horizontal plane of a tie rod for the wheel which is located radially inwardly in relation to a turning circle from that of a tie rod for the wheel which is located radially outwardly in relation to the turning circle. However, this may cause a problem in which the length of the tie rod and the position of a rack for driving the tie rod are restricted, so that the degree of design freedom regarding the steering system is reduced.